1. Field of the Invention
The present invention relates to a connecting structure of a high tension connection portion of an ignition device for an internal combustion engine.
2. Description of the Related Art
FIG. 8 is a side elevational view having a partial cross section showing a conventional connecting structure of a high tension connection portion. In FIG. 8, a high tension cable 3 is provided between an ignition plug 4 and an ignition coil (not shown) to electrically connect the two components with each other.
An ignition plug cap 1 is provided on the side of the ignition plug 4 of the high tension cable 3. The ignition plug cap 1 has a cap 1a made of rubber and a high tension connection terminal 2 formed into a cylindrical shape made of metal and embedded inside the cap 1a. An ignition plug fixture member 2a is provided on the connection side of the ignition plug 4 of the high tension connection terminal 2. Also, the other side of the high tension connection terminal 2 is press-fitted to the high tension cable 3.
The ignition plug fixture member 2a is formed as follows. Namely, first of all, round holes are formed at two diametrically opposite positions of the cylinder of the high tension connection terminal 2. A C-shaped member formed by curving an elongated steel plate in the longitudinal direction so as to cover these round holes. Projections directed inwardly toward both end portions corresponding to the round holes at the two positions of the high tension connection terminal 2 are formed on the C-shaped member. These projections are formed with top portions projecting inwardly of the high tension connection terminal 2 from the round holes. The C-shaped member has a hard elasticity and the projections are retractable from the round holes.
A head portion of the ignition plug 4 is inserted and engaged to the ignition plug fixture member 2a. If the ignition plug 4 is inserted in the axial direction with a predetermined force, the ignition plug is click-engaged with the ignition plug fixture member 2a. Also, if the ignition plug is drawn out with a predetermined force, it is removed away from the ignition plug fixture member 2a. 
On the other hand, a high tension boot 6 is provided on the side of the ignition coil of the high tension cable 3. The high tension boot 6 has a cap 6a made of rubber substantially in the form of a cylinder and a connection terminal 6b made of metal provided to project toward a center of the cap 6a. 
A high tension tower 5 is provided to the ignition coil (not shown). The high tension tower 5 has a sleeve portion 5a made of resin substantially in the form of a cylinder and a connection terminal 5b made of metal with a U-shaped cross-section and embedded in an inner surface and a bottom surface of the sleeve portion 5a. 
The sleeve portion 5a of the high tension tower 5 is inserted and engaged between the cap 6a of the high tension boot 6 and the connection terminal 6b . The connection terminal 5b of the high tension tower 5 is connected so as to cover the connection terminal 6b of the high tension boot 6.
The thus constructed high tension cable 3 electrically connects the ignition plug 4 and the ignition coil (not shown) with each other, and applies to the ignition plug 4 an ignition voltage generated in the ignition coil to thereby ignite the mixture within a cylinder of the internal combustion engine.
Conventionally, in general, it is known that if fuel is burnt within a cylinder of the internal combustion engine, an ion is generated. Then, if a probe to which a predetermined voltage is applied is provided within the cylinder, it is possible to observe the ion as an ionic current. Also, if a knock is generated within the internal combustion engine, a knock vibratory component is superimposed on the ionic current. It is therefore possible to detect the generation of the knock by extracting the vibratory component.
Recently, the device is proposed in which the ignition plug 4 is used as a probe for the detection of the ionic current, and a judgement of absence/presence of the knock is performed on the basis of the amount of the ionic current to be detected immediately after the ignition.
In the connecting structure of the high tension connection portion shown in FIG. 8, the ignition plug fixture member 2a of the high tension connection terminal 2 has a function to fix the head portion of the ignition plug 4 in place. However, a small clearance is present between the ignition plug fixture member 2a and the ignition plug 4. In the case where the ignition plug 4 is used for the normal purpose of ignition, the ignition voltage is in the range of about several kV to several tens of kV. Accordingly, even if there is a small clearance therebetween, there is no problem because the conduction may be taken due to the insulation fracture.
However, in the case where the minute ionic current is detected for the above-described purpose, even the slight clearance would affect significantly as the resistance. In particular, when an external force works to the connection portion, there is a fear that an instantaneous wire brake condition would be generated. Due to this problem, there is a problem in that the ionic current is not correctly detected.
On the other hand, on the side of the ignition coil side, the connection terminal 5b of the high tension tower 5 and the connection terminal 6b of the high tension boot 6 are connected to each other only with a frictional resistance. In the case where an external force is applied thereto, a minute sliding movement is generated at the connection portion. Then, due to the minute sliding movement, there is a problem in that an insulation coating film such as an oxygen film or the like would be formed between the two components.
Furthermore, in the same manner as in the ignition plug cap 1, due to an external force, there is a fear that the instantaneous wire break condition would be generated in the connection portion between the connection terminal 5b and the connection terminal 6b. Thus, it is impossible to use the conventional structure as the path for the ionic current.
The present invention has been made in order to overcome the above-described shortcoming, and therefore has an object to provide a high tension connection portion structure for an ignition device for an internal combustion engine, which may prevent an instantaneous breakdown even if an external force is applied to a high tension connection portion, may enhance a connection property of the connection portion by suppressing a sliding movement between metal terminals of the connection portion and may be applied to a path of a minute current such as an ionic current or the like.
In order to achieve the above object, according to one aspect of the present invention, there is provided a high tension connection portion structure of an ignition device for an internal combustion engine, comprises a first high tension connection terminal; a second high tension connection terminal for electrically connecting with the first high tension connection terminal; a lock structure provided between the first high tension connection terminal and the second high tension connection terminal for restricting the separation therebetween; and a spring member disposed between the first high tension connection terminal and the second high tension connection terminal.
According to another aspect of the present invention, there is provided the high tension connection portion structure of an ignition device for an internal combustion engine, wherein the first high tension connection terminal has an outer electrode having a recess type engagement portion into which the second high tension connection terminal is to be inserted, and the spring member is disposed inside of the recess type engagement portion between the recess type engagement portion and the second high tension connection terminal.
According to still another aspect of the present invention, there is provided the high tension connection portion structure of an ignition device for an internal combustion engine, wherein the spring member is enlarged so that a diameter of a part thereof is substantially equal to an inner diameter of the outer electrode.
According to a further aspect of the present invention, there is provided the high tension connection portion structure of an ignition device for an internal combustion engine, wherein an end portion of the spring member holds at least one of the first high tension connection terminal and the second high tension connection terminal.
According to a still further aspect of the present invention, there is provided the high tension connection portion structure of an ignition device for an internal combustion engine, wherein the recess type engagement portion has a cylindrical portion, and the second high tension connection terminal has an insulating retainer portion for holding an outer circumferential portion of the cylindrical portion.